But the Blues grabbed an equaliser when Alvaro Pereira scored an own-goal under pressure from Mario Balotelli.

Aguero - on for Balotelli - then grabbed the winner five minutes from time after being set up by Yaya Toure.

The return game is at the Etihad Stadium next Wednesday.

Victory

It was the Blues’ finest European night for some time as they turned over a team which rarely loses in their impressive stadium, even though they were some way below their best.

Porto have proven Euro pedigree – they have won the Champions League, Uefa Cup and Europa League within the last nine years, are seasoned campaigners, and notoriously hard to beat in their home town.

City won it without really hitting top gear, but at times matters descended into ugliness as sections of the Porto crowd three times appeared to aim monkey chants at Balotelli.

With Uefa observers at the stadium, that could land the club in trouble, and rightly so.

The match began at a slow pace, as if City were happy to await the second leg, while Porto were showing them a tad too much respect.

It clearly wasn’t what Roberto Mancini had in mind, as he picked a remarkably strong team, perhaps only Aguero away from his best eleven.

Back came Yaya Toure and Mario Balotelli, and it seemed as though Mancini was intent on securing a result in the first leg which would make next Wednesday’s second leg academic.

But the Blues misfired in the first half, and it was Balotelli who uncharacteristically squandered their best chance, moments after Varela had put the Portuguese side ahead.

The young Italian found himself clean through on goal as Porto’s offside trap malfunctioned and Samir Nasri lofted a fine pass to him. With just the keeper to beat, he swung a casual leg and keeper Helton was able to beat it away.

That typified a laid-back approach by the Blues. Perhaps the warm Portuguese sunshine in the afternoon had seeped into their bones.

The sun-drenched afternoon had given way to a cold night on the Bay of Biscay, and the chill reality of the task facing City was starting to bite.

The defence was equally sloppy. Big central defender Rolando was allowed a free header from James Rodriguez’s corner and Gael Clichy had to head up and away with Joe Hart beaten, for the game’s first chance after a dull opening 15 minutes.

Yaya, back after a six-week absence on African Nations Cup duty, made an impact of sorts when a trademark charge upfield saw him up-ended by a crude Danilo challenge.

The defender, who Mancini admitted on Wednesday he had “watched” for a year, was stretchered off, and had a yellow card waved in his direction as he went.

Close

The Blues came close to a lead when a free kick routine momentarily unhinged an unconvincing Porto rearguard. Nasri fired the free kick centrally into the box and Balotelli arrived from wide to flick a header goalwards.

Helton, panicked by the contact, beat it away and when Porto failed to clear their lines Micah Richards crashed in a shot which the keeper had to turn round.

City were getting into their stride and when David Silva spread a gorgeous pass to Nasri in space on the right, the Frenchman again forced Helton to turn a shot round the post.

But Porto are unbeaten in their domestic league for more than three years, and had not lost a European game at the Estadio do Dragao in seven matches.

The kind of belief a record like that gives you began to show, although Mancini will be less than impressed with the City defending.

The Blues have been working hard at defensive situations on the training ground as the season reaches a tight, tense climax.

But Richards allowed Hulk too much space on the left, and when his near-post cross was fired in Varela darted in and produced a shot which Hart could not keep out.

Then came Balotelli’s golden chance, and its overly casual ending, which took some of the wind out of the Blues’ sails.

The Blues needed a strong start to the second half and when strength is needed, Richards is a good port of call. He powered forward on the overlap and slammed a shot against the post, Helton again looking a trifle startled.

City kept up the pressure, and one bewildering move, naturally involving Silva but with the killer pass coming from Gareth Barry, found Balotelli in space. This time his control let him down, although Barry’s pass had real pace on it.

But this was much more like it, and on 56 minutes the Blues were level, albeit with a slice of luck.

Yaya’s raking ball in to the box was aimed for Balotelli’s run, and when he collided with Alvaro Pereira, the ball struck the Porto defender and flashed past the stranded Helton.

Porto had been pinned back at the start of the second half, but with their pride stung Porto hit back hard.

Kompany, Nigel de Jong and Barry were all booked in the space of two minutes, and Hart was forced to beat away a blockbuster of a free kick by Hulk as the home side sought the winner.

Porto, to their great discredit, wasted energy and time trying to get one of City’s four booked players sent off, with some ridiculous histrionics, but to be fair to Turkish ref Cuneyt Cakir – who sent off Balotelli in last season’s game with Dynamo Kiev – he was having none of it.

And City scored again six minutes from time, as Barry slipped a pass through for Yaya, and he unselfishly squared for Aguero – on for Balotelli – to tap into the empty net.
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